Ultrasound system with dynamically automated doppler flow settings as a sample volume is moved

ABSTRACT

An ultrasound system performs duplex colorflow and spectral Doppler imaging, with the spectral Doppler interrogation performed at a sample volume location shown on the colorflow image. The colorflow image is displayed in a color box overlaid on a co-registered B mode image. A color box position and steering angle processor analyzes the spatial Doppler data and automatically sets the color box angle and location over a blood vessel for optimal Doppler sensitivity and accuracy. The processor may also automatically set the flow angle correction cursor in alignment with the direction of flow. In a preferred embodiment these optimization adjustments are made automatically and continuously as a user pauses at points for Doppler measurements along a length of the blood vessel.

This invention relates to ultrasonic diagnostic imaging systems and, inparticular, to ultrasound systems with automated Doppler flow settings.

Ultrasound imaging systems are operable in B mode for tissue imaging,and Doppler modes for flow analysis and imaging. Typical Doppler modesinclude the power Doppler mode used for both tissue motion and flowimaging, colorflow Doppler for qualitative flow imaging, and spectralDoppler for flow quantification. Doppler can be performed in onedimension (M mode and spectral Doppler), two dimensional imaging, andthree dimensional imaging.

Current diagnostic ultrasound systems offer a number of acquisitioncontrols for the user to manipulate in order to achieve the optimalimage quality to help with the patient diagnosis. During vascular exams,users frequently use the colorflow Doppler imaging mode to assess anddiagnose blood vessels. Users frequently manipulate the color boxposition to center it on a vessel of interest and manipulate the Dopplersample volume to locate it on the vessel sites of interest to acquire aspectral Doppler waveform of a particular location in the body. Usersalso manipulate the Doppler angle correction control to align the flowdirection cursor with the vessel orientation. Proposals have been madeto automate the placement of the flow angle cursor over the blood flowof a vessel as shown by U.S. Pat. No. 6,464,637 (Criton et al.), WO96/17549 (Goujon), U.S. Pat. No. 6,068,598 (Pan et al.), and U.S. Pat.No. 6,176,830 (Freiburger). Freiburger also discusses automaticplacement of the Doppler sample volume based upon the detected locationof maximum velocity in an image, setting the pulse repetition frequency(PRF) based upon the maximum detected frequency shift, and automaticallysetting the gain based upon the amplitude of colorflow data. U.S. Pat.No. 6,126,605 (Washburn et al.) automatically adjusts thresholds anddata compression for a Doppler image by using histograms and samplingsof colorflow data, and U.S. Pat. No. 6,322,509 (Pan et al.) adjusts theDoppler sample volume position and size based on image data of a bloodvessel. WO 03/19227 (Christopher et al.) describes automatic settings ofspectral Doppler and colorflow Doppler displays based upon both spectralDoppler and colorflow Doppler information.

To obtain consistent velocity measurements for multiple exams of thesame patient or to compare measurements of different patients, users tryto maintain a fixed Doppler angle, the angle at which the Doppler beamsare transmitted in relation to the direction of flow, and there are twoapproaches to achieving this goal. One approach is to fix the anglecorrection cursor over the image and heel-toe manipulate the transducerto align the vessel with the angle line. Another approach is to rely onultrasound systems offering a feature that adjusts the beam steeringangle each time the angle correction is changed by the user to achieve afixed Doppler angle. However the angle correction is still donemanually. What is needed is an ultrasound system which automaticallyadjusts the beam steering angle and the color box in which Dopplerinterrogation is performed based upon the characteristics of the bloodvessels in the image, and to do so automatically whenever thesonographer moves the sample volume to a new location for a spectralDoppler measurement.

In accordance with the principles of the present invention, a diagnosticultrasound system is described which automates the color box placement,Doppler sample volume placement, angle correction, and beam steeringangle using vessel segmentation and flow image analysis. In a preferredembodiment the automation is carried out each time the user indicates apoint in a blood vessel for flow analysis, without the need to adjustany user controls. The optimal ultrasound transmit and viewingparameters are determined and set automatically each time the userindicates a new location for diagnosis, eliminating the time consumingand tedious adjustments otherwise necessary for every selection of a newsite of interest. Ergonomic-related injuries from repeated controlmanipulation are reduced, particularly in the scanning of long vesselssuch as the carotid artery and lower extremity vessels.

In the drawings:

FIG. 1 illustrates in block diagram form a diagnostic ultrasound systemconstructed in accordance with the principles of the present invention.

FIG. 2 is a flowchart illustrating the operation of the color boxposition and steering angle processor of FIG. 1.

FIGS. 3 a and 3 b illustrate the segmentation and analysis of a bloodflow image of a blood vessel.

FIGS. 3 c and 3 d illustrate the automatic repositioning of a color boxin accordance with the principles of the present invention.

FIGS. 4 to 7 are a sequence of ultrasound system displays illustratingan implementation of the present invention.

FIG. 8 is an ultrasound system display illustrating controls forautomatic flow tracking in accordance with the principles of the presentinvention.

FIGS. 9 and 10 are ultrasound system displays showing automatic trackingof a sample volume, color box placement, and angle correction during anultrasound exam without user intervention.

Referring first to FIG. 1, an ultrasound system constructed inaccordance with the principles of the present invention is shown inblock diagram form. An ultrasound probe 10 contains a transducer array12 of transducer elements which transmit ultrasound waves into the bodyand receive returning echo signals. The transmitted waves are directedin beams or scanlines to interrogate a region of interest in the body. Aone-dimensional array can be used to transmit beams over a single planefor two dimensional imaging, or a two-dimensional array of transducerelements can be used to transmit beams over a volumetric region of thebody for three dimensional imaging. The beams can be steered and focusedin different directions by the probe to interrogate tissue in specificlocations or blood flow in specific directions as explained more fullybelow. Control and processing of beams on transmit and receive isprovided by a beamformer controller 16, which controls a beamformer 14,connected to the elements of the transducer array 12, to transmitproperly formed beams and beamform the received signals through delayand summation into coherent echo signals. The beamformer can control thetransducer array to scan beams over a desired image plane, for example,and to repetitively scan beams over an area of the image plane in whichblood flow is to be assessed at a PRF appropriate for the velocities ofblood flow present in that region of the body.

A quadrature bandpass filter 18 processes the echo signal intoquadrature I and Q components. The separate components are used by aDoppler angle estimator to estimate the phase or frequency shift of aDoppler signal at points where Doppler interrogation is to be performed.The B mode detector uses the I and Q components to perform B modedetection for tissues images by taking the square root of the sum of thesquares of the I and Q components. The detected echo intensities areprocessed on a spatial basis to form a two or three dimensional image ofthe tissue in the body, which is processed for display by displayprocessor 36 and displayed on display screen 52.

The Doppler frequencies at locations in the image plane which areproduced by the Doppler angle estimator 20 can be mapped directly tovelocity values of flow at those locations. This Doppler data is coupledto a colorflow processor 30 which spatially processes the data into atwo or three dimensional image format, in which the velocity values arecolor-coded. This Doppler color map is overlaid over the spatiallycorresponding B mode image by the display processor 36 to illustrate thelocations in the anatomy where flow is taking place and the velocity anddirection of that flow by the color coding. Doppler data from aparticular point in the image, selected by placement of a sample volumeover that location in the image, is coupled to a spectral Dopplerprocessor 32 which produces a spectral display of the variation anddistribution of flow velocities at that point with time. The spectralDoppler display is forwarded to the display processor 36 for processingand display of the spectral Doppler display on the display screen 52.

In accordance with the principles of the present invention, colorflowdata from the colorflow processor 30 and, preferably, B mode data fromthe B mode processor 24, is coupled to a color box position and steeringangle processor 40. The color box position and steering angle processorcontrols the automation of settings and features of the colorflow image,including properly positioning the color box, setting the Doppler angleof the Doppler beams, locating the sample volume in the image, andproper positioning of the flow angle cursor. For control of the Dopplerangle the color box position and steering angle processor is coupled tothe beamformer controller 16 to control the Doppler beam directions.Setup and control of the automation provided by the color box positionand steering angle processor is provided by the setting of controls on auser control panel 50. Graphical display of functions controlled by thecolor box position and steering angle processor, such as the outline ofthe color box and the flow angle cursor, is provided through a graphicsprocessor 34 which is coupled to the display processor 36 to overlay thegraphics over the ultrasound images.

The operation of the color box position and steering angle processor 40is illustrated by the flowchart of FIG. 2. The first step 102 in theprocess is to segment the flow in an ultrasound image spatially. Thismay be performed by masking out areas of an image where flow does notoccur. In a given implementation the Doppler image from the colorflowprocessor may provide a spatial image of only the flow locations in theimage. This step may also include averaging the flow data over some orall of the heart cycle to produce average or median flow values. In step104 the blood vessels are segmented, separating them from other motionaleffects such as perfusion or tissue motion. In step 106 a vessel ofinterest is selected. A vessel of interest will generally be located inthe center of the image acquired by the user. A vessel of interest mayalso be selected by considering the size, flow, and type of bloodvessels which have been segmented. In a carotid exam, for instance, thecarotid artery will be identified as an artery and as the largest vesselin the image. FIG. 3 a shows an actual ultrasound flow image 120 of theflow in blood vessels which has been segmented and selected for furtherprocessing.

In step 108 the center of the flow path of a vessel is identified.Several techniques for plotting the center of the flow path are known,such as locating the center of the laminar flow field by velocity.Another technique is to analytically draw lines across the blood vessellumen as shown in the aforementioned Goujon patent application. Thecenters of the lines or their points of intersection define the centerof the vessel. FIG. 3 b illustrates the vessel flow of FIG. 3 a in whichthe center of the flow path has been identified by the white tracing122. This example shows the branching of a connecting vessel at thebottom of the image. In step 110 the flow-weighted center of mass iscalculated. This is done by analyzing the spatial dimensions of the flowin the target vessel and finding its center. A simple approach is tomeasure the length and width of the flow of the vessel and take thecenter of each. More sophisticated approaches of weighting andintegration may also be used.

In a system where the sample volume is to be set automatically, theprocess next sets the sample volume location in step 112 as the point onthe flow path 122 which is closest to the calculated center of mass.This positions the sample volume generally in the center of the image ofthe blood vessel and in the center of the vessel where flow measurementsare generally taken. In step 114 the flow angle is set in accordancewith a flow vector localized to the sample volume location. One of thetechniques described at the outset of this patent may be used to set theflow angle cursor orientation. Another approach is to set the flow anglecursor to be parallel to the center line 122 as the center line isoriented in the vicinity of the sample volume.

Using the center of mass of the flow previously calculated in step 110,the color box is positioned to be centered about the center of mass. Ifthe center of mass is too close to the side of the image, some of thecolor box area may be truncated as needed. The color box may also berescaled in height or width if desired for a uniform appearance. FIGS. 3c and 3 d illustrate such a repositioning of a color box 70 in anultrasound image 60. In FIG. 3 c the flow region 76 is the smooth greyregion in the blood vessel at the top of the color box 70. Thecomputation of the center of mass of the flow 76 and its repositioningto the center of the color box 70 is shown in FIG. 3 d, in which thecolor box has been relocated so that the flow 76 is more centered in thecolor box. In step 118 the color box steering angle and the angle of theDoppler beams is set to achieve a desired Doppler angle. For instance ifthe flow angle set in step 114 shows that the target vessel flow is fromthe upper left to the lower right in the image, the steering angle willbe set to angle from the upper left to the lower right. This steeringdirection is more nearly in line with the flow direction than a steeringangle directed from the upper right to the lower left of the image,which would be more closely orthogonal to the flow direction and henceless sensitive to Doppler flow. A typical steering angle for superficialvessels is ±60°. The setting of step 118 would then set the steeringangle to be +60° or −60°, whichever will produce the better Dopplersensitivity. Such a resetting of the color box steering angle is alsoseen by comparing the color box angle in FIG. 3 c with the reset anglein FIG. 3 d. This setting of the color box steering angle may be set inaccordance with the local flow direction at the sample volume location,or in accordance with average or median flow angles along some or all ofthe displayed length of the blood vessel. With the color box angle thusreset, the new setting of the angle is coupled to the beamformercontroller 16 so that the ultrasound beams transmitted to the color boxwill be transmitted at the newly determined angle.

The sequence of images of FIGS. 4-7 illustrate an example of how theultrasound system described above can operate. FIG. 4 shows anultrasound system display of a typical colorflow/spectral Doppler dupleximage with non-optimized Doppler settings. The anatomical ultrasoundimage 60 is at the top of the screen and the spectral Doppler display 62is at the bottom of the screen. Doppler interrogation is done inside thecolor box 70, and a colorflow image is displayed inside this box.Outside the color box 70 the rest of the image is shown in B modegrayscale. The use of a color box delineates the region where Doppler isto be performed, and repeated Doppler transmission for Doppler ensembleacquisition is not performed outside of the color box. Restricting theDoppler transmission to only the color box eliminates the need forrepeated line interrogation outside the box and hence limits the totalnumber of transmit-receive cycles needed to produce the image, therebyreducing the time needed to acquire the image which improves the realtime frame rate of display. The Doppler beams for the spectral Dopplerdata are transmitted and received along the beam direction line 68 andthe data used for the spectral Doppler display are acquired from echoesreturning from the sample volume SV on the beam direction line. TheDoppler flow direction cursor 66, used for angle correction, is notaligned with the orientation of the vessel 64 (it should be parallelwith the flow direction), and the Doppler steering angle is notoptimized for the best color and spectral Doppler sensitivity. In thisexample the Doppler steering angle is 0°, vertical in the image andnormal to the face of the transducer probe.

FIG. 5 shows the ultrasound system display after several of theautomatic adjustments of the present invention have been made by thecolor box position and steering angle processor 40. After the user hasplaced the Doppler sample volume SV on the site of interest in the bloodvessel 64, the processor 40 segments the blood flow of vessel 64 andeasily identifies vessel 64 (step 106) as the target vessel, the largestvessel in the color box 70. The center of the flow path is identified(step 108) and the orientation of the flow direction cursor 66 is set tobe parallel to the flow direction (step 114) as FIG. 5 illustrates. Itis also seen that the angle of the color box 70 and beam direction line68 have been set to achieve a 60° angle with the orientation of vessel64 (step 118). The new setting will produce better Doppler sensitivityand accuracy due to the more optimal settings.

FIG. 6 illustrates a scenario in which the user has moved the samplevolume SV to a different location over the blood vessel 64. Theautomated system has responded by calculating the center of mass of theflow in the vessel 64 inside the color box 70 (step 110). The color box70 has been repositioned so that the box is centered on the calculatedcenter of mass (step 116); the sample volume SV is in the center of thecolor box 70. The angles of the flow direction cursor 66 and the beamdirection line 68 and color box 70 have also been adjusted to achievethe desired 60° Doppler angle between the beam directions and the flowdirection.

In FIG. 7 the user has changed the image view by moving the ultrasoundprobe and has repositioned the sample volume SV to a different vesselabove vessel 64. The calculations based upon the the previously selectedvessel 64 and its view now no longer apply to the new site of interest.The calculations of the flowchart of FIG. 2 must now be initializedusing new data from the different vessel in order to apply automatedadjustments to the different vessel in the new view.

FIG. 8 illustrates an implementation of the present invention in whichthe user controls for automated flow adjustment are implemented assoftkeys on the display screen and are selected and actuated through amouse or trackball control on the control panel 50. Button 82, theAutoFlow On/Off button, is actuated to turn the flow automation on oroff. Clicking this button will toggle the automated system off (if on)or on (if off). The AutoFlow Reset button 84 will reset the automationresults if the user is dissatisfied with them. Actuating this buttonwill cancel all previous calculations by the processor 40 and start themanew. The AutoFlow Config button 86 opens a menu (not shown) in whichthe user can select which of the automated adjustment features the userwants to use. The user may want to have the system automaticallyrelocate the color box and the angles of the color box and beamdirection, for example, but wants to place the sample volume cursor SVand set the orientation of the flow direction cursor manually. In thiscase the processor 40 can use the orientation of the manually set flowdirection cursor to calculate and set the color box and beam directionsteering angles, or use computed average or mean flow angles. Actuationof the AutoFlow SV Track button 88 causes the system to dynamicallytrack the sample volume as it is repositioned and continually makesautomated flow adjustments as described below.

FIG. 9 illustrates a scenario where the user has just taken Dopplermeasurements at location 80 in blood vessel 64 and wants to take aseries of measurements at different points along a section of the bloodvessel. In prior art systems, adjustments have to be made to the Doppleracquisition settings for each new measurement, requiring the user tocontinually make manual adjustments with the controls of the ultrasoundsystem. In this illustration the user is finished with the measurementsat location 80 and has moved the sample volume SV to the left to anotherlocation in the blood vessel. When the user pauses the sample volumemotion to stop at the new measurement location to the left, or clicks onthe new location, the ultrasound system immediately makes all of theautomated setting adjustments which the user has selected with theAutoFlow Config button settings. The result is illustrated by FIG. 10,where the system has automatically repositioned the color box to becentered around the new sample volume location, has automaticallyadjusted the Doppler angle of the color box 70 and the spectral beamdirection line 68, and has automatically set the angle of the flowdirection cursor 66. The system is immediately ready to acquire spectralDoppler data under optimal conditions at the new sample volume location.The exam can continue in this manner. Each time the user moves thesample volume cursor to a new location on the vessel and pauses there,or clicks on the new location, the system will automatically reset theDoppler acquisition controls for optimal data acquisition. The user cantake measurements along a continuous length of the blood vessel withoutthe need to manually readjust any of the Doppler control settings,speeding the conduct of the exam and improving the comfort andconvenience of the sonographer.

1. An ultrasonic diagnostic imaging system which produces spectralDoppler displays of flow for anatomical locations selected from acolorflow image comprising: an ultrasonic transducer array probe whichtransmits beams and receives echo signals from a region of a subjectwhere flow is present; a beamformer which controls the directions inwhich beams are transmitted by the probe; a Doppler processor responsiveto the echo signals to produce a colorflow Doppler image and a spectralDoppler image; a display on which the colorflow Doppler and spectralDoppler images are concurrently displayed; a user control which isadapted to be manipulated by a user to indicate a plurality of locationswhere spectral Doppler measurements are to be taken in a blood vesselshown in a color box that represents a boundary of the colorflow Dopplerimage; and a color box position and steering angle processor configuredto use Doppler signals from the locations to automatically position thecolor box and orient a color box steering angle as the user manipulatesthe control from one indicated location to another.
 2. The ultrasonicdiagnostic imaging system of claim 1, further comprising a user flowcontrol operable by a user to turn the automatic operation of the colorbox position and steering angle processor on or off.
 3. The ultrasonicdiagnostic imaging system of claim 2, further comprising a userconfiguration control operable by a user to determine functions to beautomated when the color box position and steering angle processor isturned on.
 4. The ultrasonic diagnostic imaging system of claim 2,wherein the user control used to indicate the plurality of locations isfurther operable to move a sample volume cursor on the colorflow Dopplerimage; and wherein the user control is operable to cause the color boxposition and steering angle processor to determine an optimal color boxlocation automatically each time the user pauses the movement of thesample volume cursor.
 5. The ultrasonic diagnostic imaging system ofclaim 1, wherein the color box position and steering angle processorautomatically changes the color box steering angle with respect to theregion of the subject where flow is present.
 6. The ultrasonicdiagnostic imaging system of claim 5, wherein the color box position andsteering angle processor is further operable to automatically determinean angle of a Doppler steering angle line that generates optimalsensitivity to the Doppler signals.
 7. The ultrasonic diagnostic imagingsystem of claim 6, wherein the color box position and steering angleprocessor is coupled to the beamformer to control the angle of Dopplerbeam transmission to be consistent with the determined Doppler steeringangle line.
 8. The ultrasonic diagnostic imaging system of claim 1,wherein the color box position and steering angle processorautomatically positions and orients the color box by determining theposition of the color box relative to the location of the blood vesselshown in an ultrasound image.
 9. The ultrasonic diagnostic imagingsystem of claim 1, wherein the color box position and steering angleprocessor automatically positions and orients the color box bydetermining the position of the color box relative to the location of aDoppler sample volume in an ultrasound image.
 10. The ultrasonicdiagnostic imaging system of claim 1, wherein the color box position andsteering angle processor is further operable to automatically set theorientation of a flow direction cursor, wherein internal angles of thecolor box are set in consideration of the orientation of the flowdirection cursor.
 11. The ultrasonic diagnostic imaging system of claim1, further comprising a graphics processor responsive to the color boxposition and steering angle processor for graphically delineating thelocation of the color box on an ultrasound image.
 12. The ultrasonicdiagnostic imaging system of claim 11, wherein the graphics processor isfurther operable to graphically delineate the locations of a Dopplersample volume graphic and a Doppler steering angle line on an ultrasoundimage.
 13. The ultrasonic diagnostic imaging system of claim 1, furthercomprising a B mode processor responsive to the echo signals to producea B mode image, wherein the colorflow Doppler image is displayed inspatial registration with the B mode image in the color box.
 14. Theultrasonic diagnostic imaging system of claim 1, wherein the color boxposition and steering angle processor is further configured to useDoppler signals from the blood vessel for determining a center of massof a flow of the blood vessel.
 15. The ultrasonic diagnostic imagingsystem of claim 14, wherein the color box position and steering angleprocessor is further operable to position the color box to be centeredabout the determined center of mass of the flow of the blood vessel.